1. Field of the Invention
This invention relates to surge suppression devices and more particularly to a fault sensor for detecting the failure of the surge suppression device.
2. Description of the Related Art
Varistors are widely used in many electronic circuits for protecting the electronic circuit against excessive transient voltages. The varistor protects the electronic circuit by shunting current created by excessive transient voltages away from sensitive components of the electronic circuit.
A varistors utilizes a surge suppression material interposed between plural metallic plates. An insulator overlies the surge suppression material as well as the plural metallic plates. A first and a second electrode extend into the insulator for connection to the plural metallic plates. The first and second electrodes are connected within an electronic circuit for providing protection against excessive transient voltages.
One of the most common varistors use in electronic circuit is the metal oxide varistor. The metal oxide varistor utilizes a mass of zinc oxide grains in a matrix of other metal oxides to form the surge suppression material. Each grain of the zinc oxide forms a diode junction with an adjacent grain which permits current to flow only in one direction. The multiplicity of randomly oriented diode junctions forms a surge suppression material. The surge suppression material is matrix of back-to-back diode pairs with each pair of diodes being in parallel with many other pairs of diodes.
When a small a moderate voltage is applied across the first and second electrodes, only a small reverse leakage current flows through the multiplicity of diode junctions. When a large voltage is applied across the first and second electrodes, the diode junctions break down because of the avalanche effect in a large current flow. The metal oxide varistor has highly non-linear voltage-current characteristic in which the metal oxide varistor has a high resistance at low applied voltage and a low resistance at applied high-voltage.
Although the metal oxide varistor has found widespread use and success in protecting electronic circuits, the metal oxide varistor suffers from certain deficiencies. If the transient voltage is higher than the design criteria of the metal oxide varistor, metal oxide varistor may melt, burn, vaporize or be totally destroyed. Nearby lightning strikes may cause such damage to a metal oxide varistor.
When the metal oxide varistor is melted, burned, vaporized or otherwise be damaged, the metal oxide varistor can cause a fire within the equipment or products the metal oxide resistors are intended to protect. A fire within the equipment or products may spread to nearby or adjacent areas possibly causing injury and/or damage to persons and property.
Typically, the melting, burning, vaporization of a metal oxide varistor produces conductive plasma. The conductive plasma provides an opportunity to detect damage or total destruction of the metal oxide varistor in real-time.
Therefore, it is a primary object of the present invention to provide a fault sensor for detecting the failure of a surge suppression device such as a metal oxide varistor.
Another object of the invention is to provide a fault sensor for detecting the failure of a surge suppression device that may be connected to disconnect circuits or circuit breakers.
Another object of the invention is to provide a fault sensor for detecting the failure of a surge suppression device that may be retrofitted into existing surge suppression devices.
Another object of the invention is to provide a fault sensor for detecting the failure of a surge suppression device that may be incorporated within the manufacture of the surge suppression device.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by modifying the invention within the scope of the invention. Accordingly other objects in a full understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment of the invention.